Chemical reactions that convert sp² to sp³ hybridization have been demonstrated to be a fascinating yet challenging route to functionalize graphene. So far it has not been possible to precisely control the reaction sites nor their lateral order at the atomic/molecular scale. The application prospects have been limited for reactions that require long soaking, heating, electric pulses or probe-tip press. Here we demonstrate a spatially selective photocycloaddition reaction of a two-dimensional molecular network with defect-free basal plane of single-layer graphene. Directly visualized at the submolecular level, the cycloaddition is triggered by ultraviolet irradiation in ultrahigh vacuum, requiring no aid of the graphene Moiré pattern. The reaction involves both [2+2] and [2+4] cycloadditions, with the reaction sites aligned into a two-dimensional extended and well-ordered array, inducing a bandgap for the reacted graphene layer. This work provides a solid base for designing and engineering graphene-based optoelectronic and microelectronic devices.

将sp ²转化为sp ³的化学反应杂交已被证明是一种使石墨烯功能化的迷人但具有挑战性的途径。到目前为止，还不可能在原子/分子尺度上精确控制反应位点及其横向顺序。对于需要长时间浸泡、加热、电脉冲或探针尖端按压的反应，应用前景受到限制。在这里，我们展示了二维分子网络与单层石墨烯无缺陷基面的空间选择性光环加成反应。在亚分子水平上直接可视化，环加成是由超高真空中的紫外线照射触发的，不需要石墨烯莫尔图案的帮助。该反应涉及 [2+2] 和 [2+4] 环加成反应，反应位点排列成二维扩展且有序的阵列，为反应的石墨烯层诱导带隙。这项工作为设计和设计基于石墨烯的光电和微电子器件提供了坚实的基础。